The study will characterize the nature of the association between socioeconomic status (SES), health behaviors and cardiovascular disease (CVD) in the existing Vietnam Era Twin (VET) registry, a sample of over 4000 male twin pairs with a mean age of 51 in 1999. Specifically, the study will: 1) determine how strongly environmental factors contribute to individual differences in SES, health behaviors and CVD, relative to genetic factors; 2) examine whether measures of SES are associated with health behaviors and CVD mortality when controlling for concomitant genetic influences; and 3) investigate whether SES interacts with genetic vulnerabilities to predict health behaviors and CVD (gene x environment interaction). Using VETdatasets, the primary method of analysis will be twin structural equation modeling.